Any practical QKD implementation suffers from imperfections, such as flaws in the source and/or detector(s). These could be exploited by an eavesdropper Eve to obtain information about the secret key without being discovered. With secure quantum communication poised to be the first successful commercially-deployed application of quantum information processing, it becomes increasingly important to verify the actual level of security in the implementations. We experimentally review an off-the-shelf commercial system from ID Quantique to identify loopholes and exploit vulnerabilities by simulating and performing attacks on it. The principal idea is to secure the system in a regenerative sense, so we also propose patches and countermeasures, wherever possible. In this project, we collaborate with the Quantum Hacking group situated at IQC Waterloo in Canada.
So far, we have been able to successfully compromise the security of the system by launching a variety of faked-state attacks. Using tailored bright illumination to blind the detectors , Eve can dictate the measurements performed by Bob and thus, obtain a perfect copy of the raw key while remaining virtually undetected. A more sophisticated version of this employs heating the APDs with bright illumination. Since this thermal blinding  can be done well in advance of the actual key-exchange frames, it is as such harder to catch. We recently also tested another method to control the detection events by sending bright pulses outside the gated region in Bob . A video abstract explaining the basic concepts behind this attack has been made by our team (see right side).
We have also been able to exploit a vulnerability in the implementation of a vital calibration sequence of this commercial QKD system that allows Eve to induce a detector efficiency mismatch (refer figure 2). We demonstrate an optimized faked-state attack on such a hacked system that would cause a QBER below 7% without any reduction in Bob’s expected detection rate for a large range of expected channel transmissions. Most recently, a generalized version of tailored bright illumination that exploits superlinear characteristics of single-photon detectors based on APDs and superconducting nanowires has also been demonstrated .
 L. Lydersen, C. Wiechers, C. Wittmann, D. Elser, J. Skaar and V. Makarov, Nature Photonics 4, 686 (2010)
 L. Lydersen, C. Wiechers, C. Wittmann, D. Elser, J. Skaar and V. Makarov, Opt. Express 18 (26), 27938-27954 (2010)
 C. Wiechers, L. Lydersen, C. Wittmann, D. Elser, J. Skaar, Ch. Marquardt, V. Makarov and G. Leuchs, New Journal of Physics 13 (1), 013043 (2011)
 N. Jain, C. Wittmann, L. Lydersen, C. Wiechers, D. Elser, Ch. Marquardt, V. Makarov and G. Leuchs, Phys. Rev. Lett. 107, 110501 (2011)
 L. Lydersen, N. Jain, C. Wittmann, Ø. Marøy, J. Skaar, Ch. Marquardt, V. Makarov and G. Leuchs, Phys. Rev. A. 84, 8 (2011)